The present invention relates to a backlight light source drive device which is placed upon the rear surface of a display panel such as a liquid crystal display panel or the like.
Normally, a plurality of backlight light sources of this type are provided. For example, with a display panel for a liquid crystal television of the 30 to 40 inch screen size class, ten to fourteen backlight light sources are provided. Furthermore, for such a light source, often a cold cathode tube (a Cold Cathode Fluorescent Lamp) is employed (hereinafter this will simply be termed a CCFL), and a high voltage of 1 to 2 kV is applied between the electrodes at both ends thereof.
On the other hand, since a high voltage from the secondary side of a transformer is applied to such a CCFL, if a circuit anomaly such as the CCFL becoming unserviceable or its connector coming off or the like occurs, then the transformer secondary side goes into the no load state and the transformer output voltage is anomalously elevated. Accordingly, if this state is not recovered from, there is a possibility that, due to this anomalous elevation of the secondary side voltage, burnout or the like of some component may occur. Thus, in a backlight light source drive device according to the prior art, there is provided a protection signal output circuit which, when the electrical current in any single tube of the backlight light source drops below a threshold value, outputs a protection signal to a control unit for completely stopping the entire operation of the backlight light source drive circuit. When this protection signal is outputted to the control unit, in the interests of safety, a control circuit stops the operation of all of the drive circuits which are respectively provided to all of the backlight light sources. In concrete terms, the drive power supply is cut off in order to stop oscillation operation (refer to Japanese Laid-Open Patent Publication 2002-134293 and Japanese Laid-Open Patent Publication H11-355960).
Furthermore, a device has been proposed (in Japanese Laid-Open Patent Publication H05-142539) in which the end of life of a CCFL is detected by decrease of the corresponding tube electrical current, and an LED is turned ON when it has thus been detected that a CCFL has come to the end of its life.
However, with the devices of the above described Japanese Laid-Open Patent Publication 2002-134293 and Japanese Laid-Open Patent Publication H11-355960, since the oscillation is stopped immediately an anomaly occurs, accordingly, with a device which employs a plurality of backlight light sources, and in which moreover backlight light source drive circuits are connected to these backlight light sources, it cannot simply be understood which of the backlight light sources or drive circuits is the faulty one. The reason why is that, with the drive circuit whose oscillation has stopped and which is accordingly in the operation stopped state, the backlight light source or drive circuit in which the anomaly has occurred appears the same as a normal backlight light source or drive circuit, both in outward appearance and in terms of electrical signals.
Furthermore, with the device of the above described Japanese Laid-Open Patent Publication H05-142539, it is arranged, when the end of life of a tube is detected by decrease of its tube electrical current, to display this condition upon a display LED. Due to this, if this device is employed in a device which uses a plurality of backlight light sources, and in which, moreover, backlight light source drive circuits are connected to these backlight light sources, then, when an anomaly occurs, it is possible to determine upon which of the backlight light sources or drive circuits the fault has occurred, by seeing whether or not the LEDs are illuminated.
However, with this device disclosed in this Japanese Laid-Open Patent Publication H05-142539, since there is not provided any protection signal output circuit for outputting a protection signal for stopping the operation of all of the drive circuits, even if an anomaly occurs, the operation of the drive circuits is continued. Furthermore, even if hypothetically this type of protection signal output circuit were to be provided, when the input power supply went OFF, the LEDs would be extinguished. In any case, with the device disclosed in this Japanese Laid-Open Patent Publication H05-142539, even if a protection signal output circuit is provided, it still is not possible to decide in which of the backlight light sources or drive circuits the fault may be present, just as in the case of the above described Japanese Laid-Open Patent Publication 2002-134293 or Japanese Laid-Open Patent Publication H11-355960.
Thus, with a backlight light source drive device according to the prior art, although a circuit for detecting decrease of tube electrical current is provided, since no protection signal output circuit has been provided; or, even if a protection signal output circuit has been provided, there has been the shortcoming that it has not been possible to decide in which of the backlight light sources or drive circuits a fault is present.
A feature of the present invention is to provide a backlight light source drive device, which makes it possible, when a fault has occurred in a backlight light source, or a connector has come loose, or a circuit fault or the like has occurred, directly to confirm visually the position of this backlight light source, and the position of the drive circuit which drives this backlight light source.
Another feature of the present invention is to provide a backlight light source drive device, with which repairs can be performed safely, and moreover with which a fault does not become aggravated during repair due to burnout of a component or the like.